As an example of a process processing of a substrate, a substrate processing apparatus which carries out film form processing using an ALD (Atomic Layer Deposition) method is known. According to this substrate processing apparatus, two (or more) kinds of raw material gases used for forming a film are alternately supplied onto a substrate in a reaction chamber one kind by one kind, the gases adsorb on the substrate one atom layer by one atom layer, and a film is formed utilizing only surface reaction. In this case, the gas supply amount of the raw material gas is controlled in flow rate by a mass flow controller (MFC) provided in a gas supply pipe.
When a film is allowed to grow on a substrate by subjecting a substrate to alternative surface reaction of vapor phase reacting materials, the faster the adsorption of the raw material gases to the substrate surface is, the shorter the time required for forming a film becomes, and the productivity is enhanced. Generally, the absorption amount is proportional to pressure×time. When an amount corresponding to the pressure×time is defined as L, if L is constant and the pressure is higher, the same amount of gas can adsorb even if the time is shorter. That is, if the pressure in the reaction chamber is rapidly increased, the raw material gas can adsorb in a short time.
Thus, in order to increase the pressure in the reaction chamber, it is necessary to supply the raw material rapidly. Normally, an MFC is used for supplying raw material gas, but since the maximum flow rate of MFC is limited, the supply speed is limited.
For this reason, it is proposed that a gas supply pipe located downstream from the MFC is provide with a gas reservoir for storing raw material gas therein.
FIG. 6 shows an example in which a gas supply pipe is provided with a gas reservoir.
As shown in FIG. 6, the gas supply pipe 51 is provided with first and second opening/closing valves 1 and 2 in front of and behind the gas reservoir 10. When raw material gas is to be supplied, the first valve 1 located between an MFC 27 and the gas reservoir 10 is opened, the raw material gas is once stored in the gas reservoir 10 and then, the second valve 2 located between the gas reservoir 10 and the reaction tube 6 which is a reaction chamber is opened. There exist only the pipe 51 and the opened second valve 2 between the gas reservoir 10 and the reaction tube 6, and in the conventional supply method using the MFC 27, there also exist the MFC 27 and the long 51 and thus, conductance of the path becomes great, and the supply speed is increased. This will be explained using an expression. The relational expression between supply speed, conductance and pressure is Q=C×(P1−P2). Here, Q represents supply speed (Pa·m3/sec), C represents conductance (m3/sec), and P1 and P2 represent pressures (Pa) in front of and behind the pipe.
Thus, if the conductance of the path is increased, the supply speed is also increased, and the raw material gas can adsorb in a short time. That is, if the gas supply pipe is provided with the gas reservoir for storing the raw material gas, the supply speed of the raw material gas to be supplied into the reaction chamber can be increased. Thus, the raw material gas can absorb in a short time, and the film forming time can be shortened.
According to the substrate processing apparatus using the ALD method, a plurality of kinds, e.g., two kinds of reaction gases are alternately supplied onto a substrate one kind by one kind, the gases are allowed to adsorb on the substrate one atom layer by one atom layer, and a film is formed utilizing the surface reaction. This step is defined as one cycle. The thickness of the film is controlled by the number of cycles of the supply of the reaction gas. For example, when the film forming speed is defined as 1 Å/cycle, in order to form a film of 500 Å film, the processing is carried out by 500 cycles. That is, an extremely thin film is formed through one cycle, a predetermined cycles is repeated to obtain a desired thickness.
The raw material gas is once stored in the gas reservoir, and the raw material gas is supplied onto the substrate from the gas reservoir at higher supply speed. For example, if one kind of raw material gas is supplied onto the substrate from a supply port of that raw material gas along a radial direction of the substrate, a film thickness of the substrate closer to the supply port of the raw material gas becomes thick, the thickness of the film is locally increased, and there is an adverse possibility that only one location of the periphery is convexed. In the next cycle, if the gases are supplied at higher supply speed from the gas reservoir using the gas reservoir, a film is formed on a portion of the substrate other than the locally thick portion (convexed portion). Thus, if the number of cycles is 500, the locally thickened portion is dispersed, and the film thickness is equalized. When a thin film is to be formed, however, if the number of cycles is less than 60, the dispersion of the locally thickened portion is inferior, i.e., the film forming operation is finished before the locally thickened portion is dispersed, and the periphery becomes uneven and the consistency of the film thickness is deteriorated in some cases.
Therefore, it is a main object of the present invention is to provide a substrate processing apparatus capable of achieving excellent consistency of film thickness when a thin film is formed.